Rhino can be a valuable tool for both the creation of 3D mesh and as a tool for conversion of parametric based geometry to polygon geometry. Rhino also imports a large number of file formats, which can be converted to the .stl file format.
Exporting to .stl
Prior to exporting to .stl format follow these diagnostic tool to check the quality of the solid.
.stl Mesh Export Diagnostics
For some rapid prototyping machines, .stl files must contain completely closed (watertight) polygon mesh objects. You might want to do this to make sure the meshes really do fit together before exporting them for use in an expensive .stl job. Use Join, then Weld (angle=180), UnifyMeshNormals to turn a group of meshes into a single watertight mesh object. Then use SelNakedMeshEdgePt to find the open (naked) edges.
When exporting NURBS objects to .stl, Rhino converts the NURBS objects to polygon mesh objects. If Rhino cannot create a closed .stl file, the Export Incomplete Solids dialog box asks if you want to export anyway.
The tolerances you set in the Document Properties dialog box, Units page do not affect the .stl export tolerance. Instead, to control .stl accuracy, use the mesh tolerance settings from the Detailed Controls section of the mesh dialog that appears during .stl export. Set the Max distance edge to srf value to the .stl tolerance you desire.
Weld Polygon Meshes
The UnifyMeshNormals command changes the direction of the surface normals of a mesh object so they all face the same direction. This command is useful for tidying up your mesh objects for export into 3D Studio.
To test if the mesh needs to be unified:
If UnifyMeshNormals does not seem to affect your mesh, explode it. Once the normals are correct, re-join the meshes.
A polygon can have two types of normals: vertex normals and a face normal. All polygons have a face normal direction, but many polygon meshes do not have vertex normals. For example, 3DFace object, all mesh primitives and all polygon meshes imported in formats other than 3DM and 3DS do not have vertex normals at all.
In general, the order of the vertices in a polygon determines the face normal direction. The order of the vertices should be either clockwise or counterclockwise. The normal direction is determined from the vertices using the right hand rule.
Select Naked Edge Points
The selected naked edge points command shows where polygon mesh vertices are not completely surrounded by faces. Joined meshes, such as are made by Mesh Box, have naked mesh edge points where the sub-meshes are joined.
To eliminate naked mesh edge points, move them to make them match in pairs, then weld them to make a single mesh that cannot be exploded. Edges that formerly rendered sharp will shade rounded, unless you use FlatShade.